Avoid analytics and logging if dialog resolves no file

This will be the case when the dialog accepts zip files. If the selected
zip image is invalid, the module will display an error and resolve
`undefined`.

lib/browser/app.js

@@ -128,6 +128,13 @@ app.controller('AppController', function(
 
   this.selectImage = function() {
     return $q.when(dialog.selectImage()).then(function(image) {
+
+      // Avoid analytics and selection state changes
+      // if no file was resolved from the dialog.
+      if (!image) {
+        return;
+      }
+
       self.selection.setImage(image);
       AnalyticsService.logEvent('Select image', {
         image: image